Curcumin (1; diferuloylmethane; 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is a yellow pigment and an active ingredient in turmeric (Curcuma Longa). Turmeric contains curcumin along with other curcuminoids such as demethoxycurcumin and bis-demethoxycurcumin.

The yellow color of turmeric is due to the presence of the highly conjugated bis-phenolic β-diketone moiety in curcumin. The β-diketone moiety exists in equilibrium between keto and enol forms, as shown for example in Scheme 1. The energy of the enol form is 6.85 kcal/mol lower than that of the β-diketone form of Curcumin 1, suggesting that the enol form of curcumin predominates in solution.

Despite a broad range of biological activity of curcumin, its low solubility in aqueous solvent and concomitant poor bioavailability hamper its use for pharmaceutical applications.